Ureteral stents are used to assist urinary drainage from the kidney to the bladder in patients with ureteral obstruction or injury, or to protect the integrity of the ureter in a variety of surgical manipulations. More specifically, stents may be used to treat or avoid ureter obstructions (such as ureteral stones or ureteral tumors) which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter.
Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney (upper) end and a bladder (lower) end. The ends may be coiled in a pigtail or J-shape to prevent the upward or downward migration of the stent, e.g., with physiological movements. A kidney coil can function as a distal retention structure, designed to retain the stent within the renal pelvis of the kidney and to prevent stent migration down the ureter. The bladder coil sits in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder coil is also used to aid in retrieval and removal of the stent.
Ureteral stents, particularly the portion positioned in the ureter near the bladder and inside the bladder, may produce adverse effects including blood in the urine, a continual urge to urinate, strangury, and flank pain accompanying reflux of urine up the stent (e.g., when voiding) as pressure within the bladder is transmitted to the kidney. In short, stents may cause or contribute to significant patient discomfort and serious medical problems.
FIG. 10 is a schematic drawing of the human urinary tract without a stent, showing the renal pelvis 19, the kidney 23, the ureter 24, and the ureteral orifices 18 opening into the bladder 20. FIG. 11 depicts a typical double-J stent 10 which comprises a small tube 12 which sits inside the urinary system and assists the flow of urine from the kidney (renal pelvis) to the bladder. FIG. 12 depicts prior art indwelling ureteral stent 10 in position. Such stents are typically made of biocompatible plastic, coated plastic, or silicone material. Tube 12 typically varies in size from 4-8 F, and it has multiple small holes throughout its length. A coiled shape pre-formed at each end (distal end 14 and proximal end 16) of the stent 10 is designed to confine its movement within the urinary system, so that it will be maintained in the desired position. The upper (kidney) end (the distal end 14) of the stent can include a distal retention structure 104. The distal end 14 may be closed or tapered, depending on the method of insertion (e.g., the use of a guidewire). The tubular stent extends through the ureteral orifice 18a and into the bladder, fixing orifice 18a open, and thereby enhancing the opportunity for reflux. For clarity, the ureter entering bladder 20 through orifice 18b is not shown. A monofilament thread 22 may be attached to the bladder end of the stent for removal, usually without cystoendoscopy.
U.S. Pat. No. 4,531,933 (“the '933 patent”) discloses a ureteral stent having helical coils at each end which are provided for preventing migration and expulsion.